GB2329204A

GB2329204A - Earth auger

Info

Publication number: GB2329204A
Application number: GB9819543A
Authority: GB
Inventors: Peter Stanley Webb
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1997-09-11
Filing date: 1998-09-09
Publication date: 1999-03-17
Anticipated expiration: 2018-09-09
Also published as: GB9819543D0; GB9719254D0; GB2329204B

Abstract

An earth auger designed to provide triaxial compression of soil comprises a core 1 tapered radially outwardly from a lower end 2 to an intermediate point 3 along its length, and a spiral flight 6 extending over at least part of that length. The spiral flight 6 progressively increases in radial width (q) and/or thickness (r) from the lower end 2 upwards. Preferably the core 1 above the intermediate point 3 tapers radially inward until the radius is appropriate for a tubular shaft 5. Also, the flight 6 can continue beyond the intermediate point reducing in diameter and/or thickness. It is preferred that the two oppositely tapered parts are symmetrical about the intermediate point 3. The core 1 may be hollow and may have a hinged or sacrificial end section 7 from where concrete can be extruded to back fill the hole as the auger is removed.

Description

Earthworking Equipment This invention relates to earthworking equipment and more particularly to augers for use in making piles and other foundation structures.

It is known that the load-bearing capacity of such foundation structures can be usefully increased if the auger which forms the hole in which concrete (and usually reinforcing steel) is to be inserted also compacts the soil that remains around the hole. Current designs of auger do so essentially by urging the soil laterally outwards, radially away from the axis of the auger.

The present invention is based on the recognition that this results in compaction in only horizontal directions ("biaxial" compaction) and that vertical compaction is also achievable.

In accordance with the invention, an earth auger comprises a core tapered radially outwardly over a length extending from the lower end of the auger to an intermediate point along its length and having over at least part of that length a spiral flight and is characterised by the fact that the said flight progressively increases in radial width and/or in thickness in an upward direction.

Preferably the core above the said intermediate point tapers radially inwardly until its radius is appropriate for a tubular shaft of the auger, and in this case the flight preferably extends beyond the intermediate point and reduces in diameter. Preferably the two oppositely-tapered parts of the auger are substantially symmetrical.

Preferably the flight tapers in both radial width and thickness, and preferably each of the tapers is uniform.

Preferably the core of the auger is hollow so that wet concrete can be passed through it, as it is withdrawn, to fill the opening that it forms. A sacrificial point or a hinged point acting as a one-way valve can be used in the conventional way to provide for free exit of the concrete.

As an indication of scale, an earth auger in accordance with the invention will generally have a core diameter at its narrowest point of at least 60 mm and possibly up to several hundred millimetres, while its overall length will generally be several metres.

The invention includes foundation-making processes in which the auger is used and the resulting foundations.

The invention will be further described, by way of example, with reference to the accompanying drawings in which each figure is a perspective sketch of one form of auger in accordance with the invention, Figure 1 showing it being driven into the soil and Figure 2 the subsequent withdrawal step.

It comprises a core 1 which is tubular and tapers outwardly from a minimum diameter x at its bottom end 2 to a maximum diameter y at an intermediate point 3 a distance z above bottom end 2 and then inwardly at the same rate so that it returns to diameter x at a point 4 a distance z above the intermediate point 3. The shaft 5 is of uniform diameter x.

The auger has a single right-hand spiral flight 6 which extends from at the bottom end 2 to the point 4 and tapers bidirectionally and uniformly in both thickness and width, having practically zero width and a minimal thickness p at each of its ends and a radial width q and thickness r at its midpoint (the intermediate point 3).

A sacrificial point 7 completes the auger.

For illustration, a medium size of auger of this design might have the following dimensions:

dimension value (mm) diameter x 150 diameter y 350 height z 450 thickness p 25 width q 125

thickness r 225 overall length 1500 In use, the auger (with the sacrificial point in place) is held in a vertical position and rotated clockwise to drive it into the ground 8. Depending on ground conditions, this may result in the formation of a hole up to about the diameter (y) of the widest part of the core and in the displacement of relatively little soil at the surface - the hole is formed predominately by triaxial compaction of the soil; or, at this stage, the hole may be little larger than the minimum diameter x if the soil is not coherent enough to support itself.

When the desired depth is reached, wet concrete 9 is pumped into the interior of the auger in the usual way and the auger is withdrawn by rotating it anticlockwise, leaving the concrete (and the sacrificial point) in the ground; since the concrete now offers support, the body of concrete will have a diameter and shape more or less closely approximating the size and shape of the largest part of the auger. If desired a reinforcing steel cage may be inserted into the wet concrete.

Claims

1 An earth auger comprising a core tapered radially outwardly over a length extending from the lower end of the auger to an intermediate point along its length and having over at least part of that length a spiral flight and characterised by the fact that the said flight progressively increases in radial width and/or in thickness in an upward direction.

2 An earth auger as claimed in claim 1 in which the core above the said intermediate point tapers radially inwardly until its radius is appropriate for a tubular shaft of the auger.

3 An earth auger as claimed in claim 1 in which the flight extends beyond the intermediate point and reduces in diameter.

4 An earth auger as claimed in claim 3 in which the two oppositely-tapered parts of the auger are substantially symmetrical.

5 An earth auger as claimed in any one of claims 1-4 in which the flight tapers in both radial width and thickness.

6 An earth auger as claimed in any one of claims 1-5 in which the flight tapers uniformly in radial width.

7 An earth auger as claimed in any one of claims 1-5 in which the flight tapers uniformly in thickness.

8 An earth auger as claimed in any one of claims 1-7 in which the core is hollow.

9 An earth auger substantially as described with reference to the drawings.

10 A foundation-making processes characterised by the use of the auger claimed in any one claims 1-9.

11 A foundation made by the use of the auger claimed in any one of claims 1-8.

11 A foundation-making process substantially as described with reference to the drawings.

12 A foundation made by the use of the auger claimed in any one of claims 1-9.

Amendments to the claims have been filed as follows 1 An earth auger comprising a core tapered radially outwardly over a length extending from the lower end of the auger to an intermediate point along its length and having over at least part of that length a spiral flight and characterised by the fact that the said flight progressively increases both in radial width and in thickness in an upward direction.

5 An earth auger as claimed in any one of claims 1-4 in which the flight tapers uniformly in radial width.

6 An earth auger as claimed in any one of claims 1-5 in which the flight tapers uniformly in thickness.

7 An earth auger as claimed in any one of claims 1-7 in which the core is hollow.

8 An earth auger substantially as described with reference to the drawings.

9 A foundation-making processes characterised by the use of the auger claimed in any one claims 1-8.

10 A foundation-making process substantially as described with reference to the drawings.